By LEE BOWMAN, SCRIPPS HOWARD NEWS SERVICE

Updated 10:00 pm, Tuesday, March 7, 2006

When it comes to coffee consumption and heart-attack risk, a new study suggests that what's important is how quickly your body breaks down caffeine.

Research on non-fatal heart-attack patients in Costa Rica between 1994 and 2004 found that those with a gene variant that causes them to slowly metabolize caffeine have about a third greater risk of having a heart attack when they drank two or three cups a day, and 64 percent increased odds if they had four or more cups a day, compared with those who drank less than one cup a day.

Similar consumption rates in people with a gene variant that causes them to process caffeine quickly actually reduced the odds of a heart attack by 22 percent and 1 percent, respectively.

Although coffee is a major source of caffeine, previous studies that have sought to measure a link between consumption and heart attacks have been inconclusive.

It's known that caffeine raises the heart rate, and may be linked to high blood pressure. But it hasn't been clear in other studies whether caffeine alone or perhaps other chemicals found in coffee might contribute to heart-attack risk.

"Depending on your ability genetically to detoxify caffeine, your response might be quite different than someone else," said Ahmed El-Sohemy, an assistant professor of nutrition science at the University of Toronto. He led the study, published today in The Journal of the American Medical Association.

The difference is in which variant of a gene called CYP1A2 someone carries. For those with the slow-processing variant, "the amount of caffeine that lingers in the system is much greater," El-Sohemy said.

"So, one cup of coffee for them might be the equivalent of four cups for the fast metabolizers."

Working with Costa Rican researchers, the team matched up 2,014 patients who had suffered a first acute -- but non-fatal -- heart attack over a 10-year period with 2,014 healthy but otherwise similar controls.

All were tested to see which gene variant they had, and questioned about food and drink consumption and other health habits, including smoking.

Fifty-five percent of the heart-attack patients and 54 percent of the control group were slow caffeine metabolizers; the rest carried the faster variant.

Within the slow-metabolizing group, the risk from increased coffee consumption was actually greater for younger individuals. The risk associated with drinking four or more cups a day compared with less than a cup a day increased twofold for those younger than 59 to more than fourfold for those younger than 50.

El-Sohemy said that since the association between coffee and heart attacks was found only among individuals with impaired caffeine metabolism, "it strongly suggests that caffeine plays a role" in heart-attack risk.